Spinal cord stimulation (SCS) is a well-accepted clinical method for reducing pain in certain populations of patients. Spinal cord stimulator and other implantable tissue stimulator systems come in two general types: radio-frequency (RF)-controlled and fully implanted. The type commonly referred to as an “RF” system includes an external RF transmitter inductively coupled via an electromagnetic link to an implanted receiver-stimulator connected to one or more leads with one or more electrodes for stimulating tissue. The power source, e.g., a battery, for powering the implanted receiver, as well as control circuitry to command the receiver-stimulator, is contained in the RF transmitter—a hand-held sized device typically worn on the patient's belt or carried in a pocket. Data/power signals are transcutaneously coupled from a cable-connected transmission coil connected to the RF transmitter and placed over the implanted receiver-stimulator. The implanted receiver-stimulator receives the signal and generates the stimulation. In contrast, the fully implanted type of stimulating system contains the control circuitry, as well as a power supply, e.g., a battery, all within an implantable pulse generator (IPG), so that once programmed and turned on, the IPG can operate independently of external hardware. The IPG is turned on and off and programmed to generate the desired stimulation pulses from an external portable programming device using transcutaneous electromagnetic or RF links.
In both the RF-controlled or fully implanted systems, the electrode leads are implanted along the dura of the spinal cord. Individual wires within one or more electrode leads connect with each electrode on the lead. The electrode leads exit the spinal column and attach to one or more electrode lead extensions, when necessary. The electrode leads or extensions are typically tunneled along the torso of the patient to a subcutaneous pocket where the receiver-stimulator or IPG is implanted. The RF transmitter or IPG can then be operated to generate electrical pulses that are delivered, through the electrodes, to the targeted tissue, and in particular, the dorsal column and dorsal root fibers within the spinal cord. The stimulation creates the sensation known as paresthesia, which can be characterized as an alternative sensation that replaces the pain signals sensed by the patient. Individual electrode contacts (the “electrodes”) are arranged in a desired pattern and spacing in order to create an electrode array.
The combination of electrodes used to deliver electrical pulses to the targeted tissue constitutes an electrode combination, with the electrodes capable of being selectively programmed to act as anodes (positive), cathodes (negative), or left off (zero). In other words, an electrode combination represents the polarity being positive, negative, or zero. Other parameters that may be controlled or varied in SCS include the amplitude, width, and rate of the electrical pulses provided through the electrode array. Each electrode combination, along with the electrical pulse parameters, can be referred to as a “stimulation parameter set”.
Amplitude may be measured in milliamps, volts, etc., as appropriate, depending on whether the system provides stimulation from current sources or voltage sources. With some SCS systems, and in particular, SCS systems with independently controlled current or voltage sources, the distribution of the current to the electrodes (including the case of the receiver-stimulator or IPG, which may act as an electrode) may be varied such that the current is supplied via numerous different electrode configurations. In different configurations, the electrodes may provide current (or voltage) in different relative percentages of positive and negative current (or voltage) to create different fractionalized electrode configurations.
As briefly discussed above, an external control device, such as an RF controller or portable programming device, can be used to instruct the receiver-stimulator or IPG to generate electrical stimulation pulses in accordance with the selected stimulation parameters. Typically, the stimulation parameters programmed into the external device, itself, can be adjusted by manipulating controls on the external device itself to modify the electrical stimulation provided by the SCS system to the patient. However, the number of electrodes available, combined with the ability to generate a variety of complex stimulation pulses, presents a huge selection of stimulation parameter sets to the clinician or patient.
To facilitate such selection, the clinician generally programs the external control device, and if applicable the IPG, through a computerized programming system. This programming system can be a self-contained hardware/software system, or can be defined predominantly by software running on a standard personal computer (PC). The PC or custom hardware may actively control the characteristics of the electrical stimulation generated by the receiver-stimulator or IPG to allow the optimum stimulation parameters to be determined based on patient feedback and to subsequently program the RF transmitter or portable programming device with the optimum stimulation parameters. The computerized programming system may be operated by a clinician attending the patient in several scenarios.
For example, in order to achieve an effective result from SCS, the lead or leads must be placed in a location, such that the electrical stimulation will cause paresthesia. The paresthesia induced by the stimulation and perceived by the patient should be located in approximately the same place in the patient's body as the pain that is the target of treatment. If a lead is not correctly positioned, it is possible that the patient will receive little or no benefit from an implanted SCS system. Thus, correct lead placement can mean the difference between effective and ineffective pain therapy. When electrical leads are implanted within the patient, the computerized programming system, in the context of an operating room (OR) mapping procedure, may be used to instruct the RF transmitter or IPG to apply electrical stimulation to test placement of the leads and/or electrodes, thereby assuring that the leads and/or electrodes are implanted in effective locations within the patient.
Once the leads are correctly positioned, a fitting procedure, which may be referred to as a navigation session, may be performed using the computerized programming system to program the external control device, and if applicable the IPG, with a set of stimulation parameters that best addresses the painful site. Thus, the navigation session may be used to pinpoint the stimulation region or areas correlating to the pain. Such programming ability is particularly advantageous after implantation should the leads gradually or unexpectedly move, or in the case of a single-source system if the relative impedances of the contacts should change in a clinically significant way, thereby relocating the paresthesia away from the pain site. By reprogramming the external control device, the stimulation region can often be moved back to the effective pain site without having to reoperate on the patient in order to reposition the lead and its electrode array.
One known computerized programming system for SCS is called the Bionic Navigator®, available from Boston Scientific Neuromodulation, Valencia, Calif. The Bionic Navigator® is a software package that operates on a suitable PC and allows clinicians to program stimulation parameters into an external handheld programmer (referred to as a remote control). Each set of stimulation parameters, including fractionalized current distribution to the electrodes (as percentage cathodic current, percentage anodic current, or off), programmed by the Bionic Navigator® may be stored in both the Bionic Navigator® and the remote control and combined into a stimulation program that can then be used to stimulate multiple regions within the patient.
Prior to creating the stimulation programs, the Bionic Navigator® may be operated by a clinician in a “manual mode” to manually select the percentage cathodic current and percentage anodic current flowing through the electrodes, or may be operated by the clinician in a “navigation mode” to electrically “steer” the current along the implanted leads in real-time, thereby allowing the clinician to determine the most efficient stimulation parameter sets that can then be stored and eventually combined into stimulation programs. In the navigation mode, the Bionic Navigator® can store selected fractionalized electrode configurations that can be displayed to the clinician as marks representing corresponding stimulation regions relative to the electrode array.
The Bionic Navigator® performs current steering in accordance with a steering or navigation table. For example, as shown in Appendix A, an exemplary navigation table, which includes a series of reference electrode combinations (for a lead of 8 electrodes) with associated fractionalized current values (i.e., fractionalized electrode configurations), can be used to gradually steer electrical current from one basic electrode combination to the next, thereby electronically steering the stimulation region along the leads. The marks can then be created from selected fractionalized electrode configurations within the navigation table that can be combined with the electrical pulse parameters to create one or more stimulation programs.
For example, the navigation table can be used to gradually steer current between a basic electrode combination consisting of a cathodic electrode 3 and an anodic electrode 5 (represented by stimulation set 161) and either a basic electrode combination consisting of a cathodic electrode 3 and an anodic electrode 1 (represented by stimulation set 141) or a basic electrode combination consisting of a cathodic electrode 3 and an anodic electrode 6 (represented by stimulation set 181). That is, electrical current can be incrementally shifted from anodic electrode 5 to the anodic electrode 1 as one steps upward through the navigation table from stimulation set 161 to stimulation set 141, and from anodic electrode 5 to anodic electrode 6 as one steps downward through the navigation table from stimulation set 161 to stimulation set 181. The step size of the current should be small enough so that steering of the current does not result in discomfort to the patient, but should be large enough to allow refinement of a basic electrode combination in a reasonable amount of time.
Assuming, a current step size of 5% in the navigation table, there are literally billions of fractionalized electrode configurations that can be selected. However, due to memory and time constraints, only a limited number of fractionalized electrode configurations are stored within the navigation table. While this does not necessarily create an issue when the remote control is originally programmed by the Bionic Navigator®, if the remote control is to be reprogrammed; for example, if the patient returns to a physician's office to be refitted to improve the stimulation therapy provided by the IPG, the clinician may have to start the fitting from scratch when creating marks in the navigation mode.
In particular, while the remote control is capable of uploading the stimulation parameter sets to the Bionic Navigator® to aid in reprogramming the remote control, they may be different from any stimulation parameter sets that are capable of being generated using the navigation table due to the limited number of fractionalized electrode configurations within the navigation table; that is, the fractionalized electrode configurations currently stored in the remote control may not match any fractionalized electrode configurations stored in the navigation table because they were originally generated when the Bionic Navigator® was operated in the manual mode.
In any event, if the stimulation parameter sets uploaded from the remote control to the Bionic Navigator® do not identically match any stimulation parameter set corresponding to a fractionalized electrode configuration stored in the navigation table, it cannot be used as a starting point in reprogramming the remote control/IPG. As a result, the amount of time required to reprogram the remote control/IPG may be as long as the amount of time required to originally program the remote control/IPG with the Bionic Navigator®. Because programming the remote control can be quite complex, even when the Bionic Navigator® is operated in the navigation mode, the time lost as a result of having to reprogram the remote control/IPG from scratch, can be quite significant.
There, thus, remains a need for an improved method and system for reprogramming remote controls and other external devices used to control the electrical stimulation energy output by implantable devices.